An Infrared Spectroscopic Study on TbF3 in Solid Nitrogen and on Electroluminescent Thin Films of ZnS:TbF3

A search was carried out for the infrared spectrum of the TbF3 molecule in thin films of ZnS: TbF3 which form the active layers in efficient electroluminescent structures. The vibrational spectrum of a TbF3 molecule and an estimate of the oscillator strength were first obtained by trapping the molecule in solid nitrogen near 20°K employing matrix isolation techniques. Using the information so obtained, appropriate samples of ZnS : TbF3 were prepared by coevaporating ZnS and TbF3 onto CsI and Si, and a search was made for the TbF3 vibrational spectrum anticipating some solvent shift. The search proved unsuccessful. It is concluded that the ionic bond between the terbium and fluorine ions is significantly modified by embedding the molecule in the rather ionic ZnS lattice. This result is contrasted with the examples of OH− and CN− in the alkali halide lattices where the covalent bond of the molecule is little affected by the host.